One method of examining the gastrointestinal tract for the existence of polyps and other clinically relevant features that may provide an indication regarding the potential of cancer is performed by swallowing an imaging capsule that will travel through the entire gastrointestinal (GI) tract and view the patient's situation from the inside. In a typical case the trip can take between 24-48 hours, after which the imaging capsule exits in the patient's feces. Typically the patient swallows a contrast agent to enhance the imaging ability of the imaging capsule. Then the patient swallows the imaging capsule to examine the gastrointestinal tract while flowing through the contrast agent. The imaging capsule typically includes a radiation source, for example including a radioisotope that emits X-rays or Gamma rays. The radiation is typically collimated to allow it to be controllably directed in a specific direction during the imaging process. In an exemplary case the imaging capsule is designed to measure Compton backscattering and transmits the measurements (e.g. count rate) to an external analysis device, for example a computer or other dedicated instruments.
In a typical implementation a radio-opaque contrast agent is used so that a position with a polyp will have less contrast agent and will measure a larger back-scattering count to enhance accuracy of the measurements. Alternatively, other methods may be used to image the gastrointestinal tract.
U.S. Pat. No. 7,787,926 to Kimchy, the disclosure of which is incorporated herein by reference, describes details related to the manufacture and use of such an imaging capsule.
One challenge in estimating the distance from the imaging capsule to the inner walls of the colon is that the measurements are affected by the radiation blocking ability of the contents surrounding the imaging capsule: generally the contrast agent. The blocking ability of the contrast agent is dependent on the concentration of the contrast agent. Generally the patient can swallow a contrast agent of a specific concentration, however while advancing through the GI tract the water contained in the colon contents is absorbed by the colon leaving a less diluted solution have a higher concentration of contrast agent surrounding the imaging capsule. Additionally in some cases the patient is required to drink more contrast agent at specific times to assure proper functionality of the imaging capsule. Therefore at any specific position the concentration is not known. As a result the distance measurements may not be accurate as desired.
There is thus a need for improved methods of measuring the distance from the imaging capsule to the walls of the colon.